This invention relates to a fuel injection nozzle for injecting fuel, fed under pressure from a fuel injection pump, into a combustion chamber of an engine.
For example, as disclosed in Japanese Laid-Open Patent Application No. 1-92569, a fuel injection nozzle comprises an elongated hollow nozzle body having a closed lower end, and a needle valve mounted within the nozzle body. This nozzle body includes a fuel reservoir chamber, a tapered valve seat formed on the inner surface of the lower end portion of the nozzle body, and a plurality of injection ports formed in the lower end portion of the nozzle body. The inner ends of these injection ports are disposed at the valve seat of the nozzle body. The needle valve has a pressure receiving portion exposed to the fuel reservoir chamber, and a tapered conical abutment portion formed at its lower end portion. The needle valve is urged by a spring, so that its abutment portion is seated on the valve seat. In this seated condition, the inner ends of the injection ports are closed by the outer peripheral surface of the abutment portion. The pressure of fuel fed into the fuel reservoir chamber from a fuel injection pump acts on the pressure receiving portion to cause the needle valve to lift against the bias of the spring, so that the abutment portion is brought out of contact with the valve seat. As a result, the injection ports are opened to inject the fuel into a combustion chamber of an engine.
In the above fuel injection nozzle, the plurality of injection ports are classified into a first group and a second group. The first injection ports slanting downward are disposed at an acute angle relative to the axis of the nozzle body, and the second injection ports are disposed generally perpendicularly to the axis of the nozzle body. The fuel injection nozzle is mounted on the engine in inclined relation to the axis of an engine cylinder, and therefore it is expected that all of the injection ports are inclined at generally the same angle relative to the axis of the engine cylinder.
The above fuel injection nozzle can not fully satisfy the following two requirements which are necessary for further enhancing a combustion efficiency and for reducing the production of hydrocarbon and so on.
The first requirement is to vary the angle of injection of the fuel in accordance with the engine load, that is, the amount of injection of the fuel. When the engine load is small, so that the fuel injection amount is small, the temperature of the wall surface of the combustion chamber is low. If the fuel is caused to deposit on an inner surface of a cylinder head (which constitutes part of the combustion chamber) by a stream produced upon upward movement of a piston, the vaporization of the fuel is delayed, which causes the production of hydrocarbon and so on. Therefore, when the load is small, the fuel is required to be injected obliquely downward. On the other hand, when the load is large, the fuel is required to be injected generally laterally over a wide range.
Reference is made to the reason why the above fuel injection nozzle can not satisfy the first requirement. When the fuel injection nozzle is disposed in inclined relation to the axis of the engine cylinder, with all the fuel injection ports inclined at generally the same angle relative to the axis of the engine cylinder, the directions of injection of the fuel from the fuel injection ports are generally equal, and therefore in this case, it is clear that the first requirement can not be satisfied.
Let's consider the case where the fuel injection nozzle is disposed parallel to the axis of the engine cylinder. The inner ends of the first and second injection ports are disposed in a common plane perpendicular to the axis of the nozzle body. Therefore, when the needle valve lifts, the pressure at the inner ends of the first injection ports is equal to the pressure at the inner ends of the second injection ports, and the fuel is injected from both of the first and second injection ports regardless of the amount of lift of the needle valve (that is, regardless of the value of the load). Thus, the direction of the fuel injection can not be varied in accordance with the load. Particularly, in the above fuel injection nozzle, the direction of injection of the fuel from the second injection ports in the low-load condition is lateral, and therefore the fuel tends to deposit on the low-temperature inner surface of the cylinder head.
The second requirement is to make the fuel particles as fine as possible so as to easily vaporize the fuel. In the above fuel injection nozzle, the outer ends of the first injection ports are spaced apart from the outer ends of the second injection ports, and therefore the effect (later described) of making the fuel particles fine, as achieved in the present invention, can not be attained, and it is thought that its fuel particle size is generally the same as that achieved with conventional fuel injection nozzles.
Japanese Laid-Open Utility Model Application No. 62-87171 discloses a fuel injection nozzle comprising a nozzle body and a needle valve. The nozzle body has a tapered valve seat formed on an inner surface of a lower end portion thereof, and a small chamber provided below this valve seat. A single first injection port and a plurality of second injection ports are formed in the lower end portion of the nozzle body, and the angle of inclination of the first injection port is different from that of the second injection ports. When the fuel injection nozzle is slightly obliquely mounted on an engine, the first injection port extends generally horizontally, and the second injection ports extend obliquely downward. The inner end of the first injection port is disposed at the valve seat, and the inner ends of the second injection ports are disposed at the inner peripheral surface of the small chamber. The needle valve has at its lower end portion a tapered conical abutment portion and a throttle portion formed at the lower end of this abutment portion. When the abutment portion is seated on the valve seat, the throttle portion is extended into the above small chamber. In this seated condition, the inner end of the first injection port is closed by the outer peripheral surface of the abutment portion, and the inner ends of the second injection ports are closed by the outer peripheral surface of the throttle portion. When the needle valve lifts, the abutment portion is brought out of contact with the valve seat at an initial stage at which the lift is small, so that the first injection port is opened, thereby injecting the fuel from the first injection port toward an ignition plug. At this initial stage, the throttle portion remains received in the small chamber, and therefore the second injection ports are kept closed. When the needle valve further lifts, the throttle portion comes out of the small chamber, so that the second injection portions are opened, thereby injecting the fuel from the second injection ports.
In the fuel injection nozzle of the above Japanese Laid-Open Utility Model Application No. 62-87171, the fuel is injected laterally from the first injection port when the amount of lift of the needle valve is small, and therefore this fuel injection nozzle can not meet the above first requirement, as is the case with the fuel injection nozzle of the above Japanese Laid-Open patent application No. 1-92569. Further, since the outer ends of all the injection ports are spaced part from one another, the above second requirement can not be satisfied.
Japanese Laid-Open Utility Model Application No. 57-158972 discloses a fuel injection nozzle similar to the fuel injection nozzle of the above Japanese Laid-Open Utility Model Application No. 62-87171. This fuel injection nozzle has first and second injection ports which are inclined at the same angle. When the lift of a needle valve is small, fuel is injected from the first injection port, and when the lift is large, the fuel is injected from the first and second injection ports. In this fuel injection nozzle, the direction of the fuel injection is not changed regardless of the amount of lift of the needle valve, and therefore the above first requirement can not be satisfied. Further, since the outer ends of all the injection ports are spaced apart from one another, the above second requirement can not also be satisfied.
Technology Reports of Tohoku University (Vol. 22, No. 2, pages 157 to 164, issued Mar. 25, 1958; Editor: Engineering Department of Tohoku University; Publisher: Tohoku University) discloses a fuel injection nozzle comprising a nozzle body and a needle valve. The nozzle body has an equalizer chamber at its lower end portion, and a valve seat provided above this equalizer chamber. A plurality of pairs of first and second injection ports are formed in the lower portion of the nozzle body, and are spaced circumferentially of the nozzle body. The first injection ports extend obliquely downward relative to the axis of the nozzle body, and the second injection ports extend perpendicularly to the axis of the nozzle body. The inner ends of the first injection ports are disposed above the inner ends of the second injection ports. The inner ends of the first and second injection ports are open to the equalizer chamber. Each pair of first and second injection ports have a common outer end. In this fuel injection nozzle, since the inner ends of the first and second injection ports are open to the equalizer chamber, the fuel is injected from the first and second injection ports when the needle valve lifts, so that the fuel can be injected at a wide angle. However, the pressures at the inner ends of the first and second injection ports are equal to each other, and the fuel is injected from the first and second injection ports, and therefore the direction of injection of the fuel can be not selected in accordance with the load (the amount of the fuel injection), and the above first requirement can not be satisfied. Further, since the first and second injection ports have the common outer end, no pressure difference occurs at this common outer end, and therefore a cavitation is not produced, and it can not be expected to make the fuel particles fine. Therefore, the above second requirement can not be satisfied.